1. Field of the Invention
The present invention generally relates to a control system and method of use for controlling dynamical systems and, more particularly, to a control system and method of use for reducing cargo pendulation of transport-mounted cranes.
2. Description of the Prior Art
In a global economy, it is important to transport goods in the most efficient and expedient manner to ensure that the goods will arrive at the proper destination in a timely and cost effective manner. The transportation of goods, whether the goods be perishables, consumer goods or the like, can be transported in several different modes, including trains, trucks, cargo (container) ships and the like. Trains and trucks are efficient modes of transportation for limited uses, such as, local deliveries, cross country (intra continental) shipping, and cargoes of limited size. However, trains and trucks are limited to land based transportation, and thus have no applicability to trans-oceanic shipping.
In the case of trans-oceanic transportation, container ships are one of the most cost-effective manners of shipping cargo. This is because container ships can carry large cargoes and are capable of transporting these cargoes throughout the world. Shipping is also very economical because shipping routes are well established, and many localities have ports and other docking facilities in order to load and unload the ships"" cargo. Ships can also be used to replenish supplies on other ships (e.g., navy ships and submarines), which do not otherwise have access to ports during long operations.
It is known, however, that many localities do not have proper facilities in order to load and unload cargo at the local ports. This is partly due to the fact that many ports, especially those of third world countries, do not have the capabilities of accommodating large container ships. That is, many ports are either too small to accommodate large container ships or may be located on tributaries which are not navigable by the larger container ships. In these cases and many other such situations, both a crane ship and a smaller, lighter ship are summoned to the larger container ship outside of the port area. The crane ship is used to transfer the cargo from the container ship to the smaller, lighter ship. The smaller, lighter ship is then used to navigate the desired port for unloading of the cargo. Of course, the reverse operation can equally be used when loading a larger container ship (e.g., load cargo into the smaller, lighter ship in the port, sail the lighter ship to the larger container ship outside of the port area and transfer the cargo from the lighter ship to the larger container ship via the crane ship).
FIG. 1 shows a conventional cargo-transfer scenario. In this scenario, a crane ship 10 is transferring containers from a container ship 12 to a landing craft 14. The use of the crane ship includes moving a boom and cable in order to either load or unload the cargo, typically containers that may weigh in excess of 30 or 40 tons, from one ship to another ship. The boom either may be raised and lowered (boom luff) or rotated left and right (boom slew). These movements ensure that the boom can reach all of the containers on either ship. During the loading and unloading operations, it is not uncommon for the crane ship to also move due to sea states. These movements are both translational movements (surge, heave or sway) and rotational movements (yaw, pitch and roll), with the more severe sea state resulting in more severe translational and rotational movements of the crane ship.
The rotational and translational movements of the crane ship result in the movement of the boom tip. The movement of the boom tip then moves a hoisting cable (which hangs from the boom tip and is used to hold the container (cargo)) resulting in a container swing or pendulation. As should be readily recognized, the greater or more severe movement of the boom tip will result in a more severe swinging of the cable and hence the container. This, of course, can create a very unsafe environment, one which the operator cannot control. Thus, in moderate and high sea states, the operations of loading and unloading the ships must be suspended in order to ensure the safety of the crew and the cargo.
It is therefore an object of the present invention to provide a control system and method of use for controlling dynamical systems.
It is a further object of the present invention to provide a control system and method of use for reducing cargo pendulation of cranes.
It is still another object of the present invention to provide a control system and method of use for reducing cargo pendulation in ship-mounted cranes, rotary cranes, gantry cranes, truck-mounted cranes and other cranes which may exhibit unwanted pendulation.
According to the invention, a method of reducing cargo pendulation includes calculating an operator input position of a boom tip of the crane and determining a relative motion of the cargo on a hoisting cable suspended from the crane with reference to the boom tip of the crane. In-plane and out-of-plane delays and gains based on the relative motion of the cargo are then calculated and a correction to the operator input in an inertial frame is then calculated based on the in-plane and the out-of-plane delays and gains. Reference angles (luff and slew angles) of the boom based on the correction and the operator desired position of the boom tip and a motion of the platform are then calculated in order to compensate and reduce cargo pendulation.
In another aspect of the present invention a control system for reducing the cargo pendulation is provided. The control system has means for calculating an operator input position of a boom tip of the crane and means for determining a relative motion of the cargo on a hoisting cable suspended from the crane with reference to the boom tip of the crane. The control system further has means for providing in-plane and out-of-plane delays and gains based on the relative motion of the cargo. Means for calculating a correction in an inertial frame based on the in-plane and the out-of-plane delays and gains and means for calculating reference angles of the boom based on the correction and the operator desired position of the boom tip and a motion of the platform in order to compensate and reduce cargo pendulation are also provided.
In still another aspect of the present invention, an apparatus for reducing pendulations of cargo hoisted by cranes mounted on moving platforms has boom luff angle and slew angle motors for moving the crane, and tilt sensors to measure the movement of the platform. Encoders or tilt sensors read in-plane and out-of-plane angles of the cargo hoisting cable, boom luff angle and slewing angle of the crane and a controller determines a reference position of the suspension point of the hoisting cable (boom tip) for reducing the cargo pendulation based on the input of the tilt sensors and encoders.